Viennese paediatrician Baron Clemens von Pirquet
coined the term "allergy" (from the Greek "allos" meaning changed
or altered state and "ergon" meaning reaction or reactivity) in
1906 [ 1 ]. Von Pirquet used the
term to describe an altered reaction he had observed in patients,
which he put down to the influence of external factors, an allergen ,
on the immune system.